This application claims the benefit of Japanese Application No. 2001-205178, filed Jul. 5, 2001, in the Japanese Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium mounted on various magnetic recording apparatuses and a manufacturing method therefor.
2. Description of the Related Art
As a technology for increasing a density of magnetic recording, perpendicular magnetic recording media has attracted attention as a potential alternative to a conventional longitudinal recording method.
A perpendicular magnetic recording medium includes a magnetic recording layer of a hard magnetic material, an underlayer that directs the magnetic recording layer in a desired direction, a protective layer that protects a surface of the magnetic recording layer, and a lining layer of a soft magnetic material that causes a concentration of a magnetic flux generated by a magnetic head used to record on the magnetic recording layer.
In recent years, as a recording density of magnetic recording media based on the longitudinal recording method increases, a loss of recorded data associated with thermal instability (i.e., thermal fluctuations) increases. Conversely, it has been assumed that the thermal stability problem is less pronounced with perpendicular recording media than with a longitudinal recording method, because a stability of bits (recorded data) increases linearly with density. However, it is expected that a film thickness of the magnetic recording layer will be further reduced, rendering the current level of achieved thermal stability insufficient. There have also been demands to increase the stability of low-density recording for servo patterns or similar applications. Thus, even for perpendicular recording media, improving thermal stability is an important goal.
Because the thermal stability of the perpendicular recording medium is proportional to an uniaxial anisotropy constant (hereinafter referred to as xe2x80x9cKuxe2x80x9d), Ku can be increased to improve thermal stability. Specific examples of recent approaches to increasing Ku include a Co/Pt multilayer stacked film, a Co/Pd multilayer stacked film, a CoPt ordered alloy, a FePt ordered alloy, and use of an amorphous material, such as TbFeCo. However, manufacturing processes for multilayer stacked films are not suitable for mass production, the ordered alloys require an annealing process to ensure correct ordering, and a corrosion resistance of the amorphous material must be improved. Accordingly, all of these proposed methods pose problems that need to be solved prior to a practical use.
As previously described, Co/Pt and Co/Pd multilayer stacked films, Copt and FePt ordered alloys and similar materials, and amorphous materials such as TbFeCo, all have a high Ku, are disadvantageous for mass-producing recording media. If the recording media are to be mass-produced, a conventional CoCr-based magnetic recording material should be used to increase Ku, thereby improving thermal stability. However, the increase in Ku achieved by changing a composition of the recording material is limited. Thus, measures other than changing the composition of the recording material have been sought.
The following methods are proposed to solve the above problems: (1) An underlayer including a metal or an alloy having a hexagonal closest-packing (hereafter referred to as xe2x80x9chcpxe2x80x9d) type of crystal structure such as Ru, Ti, TiCr, Re, CoCr, CuZn, IrMo, Ir2W, MoPt, or MoRh2, which has a larger a-axis lattice constant than the recoding material used for a magnetic recording layer. A resulting magnetic recording layer including the above set forth underlayer has an increased a-axis lattice constant for a relative reduction in a c-axis lattice constant, thereby increasing magnetostriction and Ku. However, if the lattice constant differs excessively, a crystal structure (lattice constant) of the magnetic recording layer does not follow the underlayer. A ceiling for this difference is about 20%. (2) The underlayer including a metal or an alloy having a face-centered cubic lattice (hereafter referred to as xe2x80x9cfccxe2x80x9d) type of crystal structure such as Pd, Cu, Au, Ir, Pt, Rh, Ag, Ni3Al, or Co3Ti, which has an (a-axis lattice constant)xc3x971/2 larger than an a-axis lattice constant of the material used for the magnetic recording layer. Thus, the magnetic recording layer has an increased a-axis lattice constant for a relative reduction in the c-axis lattice constant, thereby increasing magnetostriction and Ku. As in (1), the upper limit of the difference between the lattice constant of the magnetic recording layer and the (a-axis lattice constant of the underlayer)xc3x971/2 is about 20%. (3) The underlayer of (1) or (2) is used and quenched immediately after a formation of the magnetic recording layer to distort the film to cause magnetostriction, thereby increasing Ku and a coercive force Hc. (4) The underlayer pf (1) or (2) is used and quickly heated immediately after the formation of the magnetic recording layer and before quenching to produce effects similar to those in (3).
As described above, according to an embodiment of the present invention, the thermal stability of the magnetic recording layer is improved to make the recording medium more reliable. Further, the present invention can be used with the conventional CoCr-based magnetic recording material to form film using conventional apparatuses. Therefore, the present invention is suitable for mass production.
These together with other objects and advantages, which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.